At present most hot air heaters burn a fuel which generally is either No. 2 fuel oil or gas, the combustion products of which pass through a heat exchanger and then are vented into the atmosphere. The air from the building or other space to be heated is passed from the cold air return through the other side of the heat exchanger and back through the building. Due to the high temperature of the gas going up the vent to the atmosphere a considerable amount of heat is lost. Generally conventional gas fired heaters are about 70 to 75% efficient while conventional oil fired heaters are about 65 to 70% efficient. The present heater generally will provide efficiencies of up to about 98% which enables a considerable reduction in the amount of fuel consumed in heating the building or other space to be heated.